The growing population of children in American cities is exposed to various neurotoxins present in urban environments which may damage their developing brains. Over the last decade, environmental health scientists have generated compelling data on neurotoxicity in animals and humans exposed to present-day air pollutants from road traffic emissions (or traffic air pollution [TAP]), including particulate matter and ozon in urban environments. Experimental animal models have demonstrated that early life exposures to these urban air pollutants result in memory impairment and long-term neurobehavioral changes. Consistent with neurotoxicological literature, previous data from both cross-sectional and longitudinal epidemiologic studies showed a wide range of adverse neurocognitive effects (including low IQ) associated with TAP exposure in school-aged or younger children. However, it remains unclear whether TAP-mediated adverse neurocognitive effects persist into later life possibly affecting academic performance and educational attainment in adolescents and young adults. Although toxicologists have revealed clear evidence of air pollution-induced neurotoxicity in the prefrontal lobe and hippocampus, epidemiologic studies have not yet examined higher cortical control functions (e.g., executive functions [EFs]; emotion regulation) as neuropsychological mediators of the adverse exposure-effects on neurodevelopment. Previous studies only provided very little insight on the likelihood of joint adversities resulting from exposures to both neurotoxic TAP and social stressors commonly experienced by urban-dwelling children. To address these knowledge gaps, the primary objectives of this application are to: (1) generate preliminary data and infrastructure needed for a planned long-term study on neurodevelopment in urban environments; and (2) develop a conceptual framework to elucidate neuropsychological pathways contributing to impaired cognition and long-term socioeconomic consequences of exposures to urban air pollutants. Specifically, we propose a longitudinal study built on an ongoing (2000- onwards) and well-characterized urban-dwelling Southern California Twin Cohort (R01MH058354) with comprehensive data on neuropsychological functions and outcomes assessed from school-age (aged 9-10) to young adults (aged 19-23). This application leverages the unique, prospectively-collected environmental data and resources of the ongoing Children's Health Study, enabling the estimation of early life (1990-onward) exposure to air pollution and detailed characterization of intra-urban TAP exposure during adolescents. Drawing from two theoretical models (cognitive vulnerability-stress response and emotional dysregulation) in mental health research, we will test the hypothesis that EFs/emotion regulation and their developmental trajectories serve as both the central target and neuropsychological mediators of subsequent adverse effects of TAP exposure on cognitive abilities and socioeconomic attainment. The successful performance of this project may greatly advance the emerging field of developmental neurosciences in urban environments.